The present invention relates to a semiconductor memory device, and more particularly, to a negative voltage generator for generating a negative voltage lower than a ground voltage in a semiconductor memory device.
A semiconductor memory device needs a negative voltage in order to use a negative word line driving scheme. According to the negative word line driving scheme, a word line driver enables a word line by supplying a high voltage (VPP) to the word line and disables the word line by supplying a negative voltage (VBBW) lower than a ground voltage (VSS) to the word line.
In other words, while the ground voltage (VSS) is generally supplied to the word line in order to disable the word line, the negative word line driving scheme supplies the negative voltage (VBBW) lower than the ground voltage (VSS) to the word line in order to disable the word line.
The negative word line driving scheme can improve refresh characteristic and other AC parameters. Specifically, if the word line is disabled using the negative voltage (VBBW) lower than the ground voltage (VSS), retention time of a cell increases, resulting in an increase of a refresh period. In addition, when a low power supply voltage (VCC) is used, a VPP burden of supplying the high voltage (VPP) can be reduced and a write recovery time (TWR) can be improved.